Highly-versatile variable-angle bone plate system

ABSTRACT

A bone plate system for internal fixation of bone fractures includes a bone plate having a plurality of bone plate holes. The holes are constructed to receive either a non-locking, locking, or variable-angle locking bone screw. The holes have discrete columns of teeth or thread segments arranged around the inner surface of the hole for engaging threads on the heads of locking and variable-angle locking bone screws. Conventional locking bone screws engage the bone plate coaxially with the central axis of the bone plate hole. Variable-angle locking bone screws can engage the bone plate at a selectable angle within a range of selectable angles relative to the central axis of the bone plate hole. The head of the variable-angle locking screw is at least partially spherical, and the thread thereon has a profile that follows the arc-shaped radius of curvature of the spherical portion of the screwhead.

CROSS REFERENCE TO RELATED APPLICATIONS

This claims the benefit of U.S. Provisional Application No. 60/955,506,filed Aug. 13, 2007, and is a continuation-in-part of pending U.S.patent application Ser. No. 10/763,689, filed Jan. 26, 2004. The entirecontents of both applications are expressly incorporated herein byreference thereto.

FIELD OF THE INVENTION

The invention relates to a bone plate system for internal bone fracturefixation. More particularly, the invention relates to a bone platesystem that includes bone plates one plate holes constructed to receivenon-locking, locking, or variable-angle one screws.

BACKGROUND OF THE INVENTION

Bone plate systems for the internal fixation of bone fractures are wellknown. Conventional bone plate systems are particularly well-suited topromote the healing of a fracture. A bone screw (also known as a boneanchor) is inserted through a bone plate hole (also known as an anchorhole) and is threaded into bone to compress, neutralize, buttress,tension bend, and/or bridge the fracture ends together and draw the boneagainst the plate. These screws, which are not secured to the bone plate(and are hereinafter referred to as “non-locking screws”), can bethreaded into bone at various angles relative to the bone plate.However, because the screws are not secured to the bone plate, theangular relationships between the plate and screws are not fixed and canchange intraoperatively and/or postoperatively. That is, dynamic loadingon the bone and bone plate from physiological conditions can cause thescrews to loosen or back out with respect to the plate. This can lead topoor alignment and poor clinical results.

Securing the screws to the plate provides a fixed angular relationshipbetween the screws and plate and reduces the incidence of loosening. Oneknown embodiment of screws that can be secured to the bone plate has ascrew thread on an outer surface of the screwhead. The thread on thescrewhead mates with a corresponding thread on the inner surface of abone plate hole to lock the screw to the plate. These screws (which arehereinafter referred to as “locking screws”) are typically insertedcoaxially with the central axis of the hole. Because the relationshipbetween locking screws and the plate is fixed, locking screws providehigh resistance to shear, torsional, and bending forces. However,locking screws are limited in their ability to compress bone fragments,which affects healing.

In sum, therefore, an interface formed by a locking screw and bone platehas high resistance to shear forces so as to maintain stability at thescrew/plate interface, but has limited ability to compress bonefragments, while an interface formed by a non-locking bone screw andbone plate effectively compresses bone fragments, but has low resistanceto shear forces that can lead to screws loosening or backing out.Accordingly, a bone plate system that combines non-locking screws withlocking screws is desirable in many clinical situations.

A known bone plate system that can accommodate both locking andnon-locking screws includes a bone plate having a plurality of threadedplate holes for receiving locking screws and a plurality of non-threadedplate holes for receiving non-locking screws. However, the non-lockingscrews in this known system are only used temporarily to keep the platein place while the locking screws are inserted. The non-locking screwsare removed after the locking screws have been inserted. Thus, the longterm benefits of combining non-locking screws with locking screws arenot obtained.

Another known bone plate system that accommodates both types of screwsincludes a bone plate with partially threaded plate holes. The partiallythreaded holes receive either locking or non-locking screws. Because theplate holes are only partially threaded, however, locking screws may notbe able to maintain the fixed angular relationship between the screwsand plate while under physiological loads. Specifically, the lockingscrews within the plate are only partially surrounded by threads andthus only partially secured. Under high stress and loading conditions,the locking plate hole may distort and allow the fixed angularrelationship between the locking screw and plate to change. This canresult in a loss of fixation or plate orientation. Additionally, becauseof the plate hole geometry, translation of the plate with non-lockingscrews is limited to one direction only. This may be disadvantageous inbone fracture reduction and manipulation.

Still another known bone plate system that accommodates both types ofscrews includes a bone plate with threaded and non-threaded plate holes.The threaded plate holes receive locking screws, and the non-threadedplate holes receive non-locking screws, each intended to remain insertedwhile the plate is implanted. However, because locking screws areeffective only when used with threaded holes, a disadvantage of thissystem is that the number and location of threaded holes in the platemay not be as desired for a particular surgical procedure. For example,there may be one or more non-threaded holes at locations where a surgeonwould prefer a threaded hole for insertion of a locking screw.

Further to the known bone plate systems mentioned above it is oftendesirable for a surgeon to be able to insert a locking bone screwthrough a bone plate hole at a surgeon-selected angle relative to thebone plate. A number of so-called “polyaxial” bone plate systems areknown. Many use a bushing located in a plate hole to lock the degree ofscrew angulation relative to the plate. In one such system, the bushingis rotatable within the plate hole. A so-called “variable-angle locking”screw is threaded into bone through the bushing and plate hole. As thescrew is threaded into bone, the threaded tapered head of the screwengages a threaded internal surface of the bushing to expand the bushingagainst the inner surface or wall of the plate hole, thereby frictionlocking the screw at the desired angle relative to the bone plate.

In another known polyaxial bone plate system, a bushing is seated at adesired angle in a plate hole. A fastening screw having an expandablehead with a threaded recess is inserted through the bushing and threadedinto bone. A locking screw is then threaded into the recess of thescrewhead to expand the head outward against the bushing to lock theselected angle of the screw relative to the bone plate.

In still another known polyaxial bone plate system, an expandable ringis positioned in the plate hole. As a bone screw with a tapered headengages the ring and is threaded into bone, the ring expands against theinner surface or wall of the hole to lock the selected angle of thescrew relative to the bone plate.

However, these polyaxial bone plate systems have multiple componentsthat can be cumbersome and tedious to manipulate during surgery and moreparticularly, for example, it is possible that the bushing or expandablering may pop out during surgery.

In view of the foregoing, it would be desirable to be able to provide animproved bone plate system that overcomes the deficiencies anddisadvantages of known bone plate systems.

SUMMARY OF THE INVENTION

The invention provides a highly-versatile variable-angle bone platesystem for fixing bone fractures. The system includes bone plates havinga plurality of bone plate holes that pass completely through the boneplate, from a top surface of the plate to a bottom bone-contactingsurface of the plate. The holes are constructed advantageously toreceive either a non-locking, locking, or variable-angle locking bonescrew. Instead of screw threads as is known in conventional bone plateholes, the inner surface of the plate holes has discrete columns ofteeth or thread segments for engaging compatibly dimensioned andconfigured threaded heads of locking and variable-angle locking bonescrews.

The invention advantageously permits conventional non-locking bonescrews of compatible size and screwhead shape to be used in the boneplate holes. Non-locking bone screws have a threaded shaft for engagingbone and a screwhead having no means or structures (e.g. threads)thereon for securing or locking to the bone plate. A non-locking screwmay be received in the bone plate hole at any desired angle, whereuponthe shaft of the screw is driven into the bone until the head of thescrew is seated as desired in the bone plate hole.

The invention also advantageously permits conventional locking bonescrews of compatible size, screwhead shape, and screwhead thread to beused in the bone plate holes. These locking bone screws have a threadedshaft for engaging bone and a screw thread on an outer surface of thescrewhead that can advantageously engage the columns of thread segmentsin the bone plate hole. Locking bone screws are received in the boneplate holes coaxial to the central axis of the hole. That is, forexample, if the central axis of the hole is perpendicular to the topsurface of the bone plate, a locking bone screw is received in a boneplate hole of the invention at about a 90 degree angle with respect tothe top surface. The shaft of the locking screw is driven into boneuntil the screwhead engages the bone plate hole, whereupon the screwheadthreads engage the columns of thread segments in the bone plate hole.The screw is then driven until the screwhead is threaded as desired intothe bone plate hole, which fixes the screw to the plate.

A variable-angle locking bone screw according to the invention isinserted through a bone plate hole and locked to the bone plate at aselectable angle within a range of selectable angles. The range ofselectable angles in one embodiment forms a cone of about 30 degreesabout the central axis of the hole. In other words, the angle of thescrew can vary from 0 degrees to about 15 degrees in any direction awayfrom the central axis of the hole. Variable-angle locking screws of theinvention advantageously do not require a bushing, a compression cap, anexpandable ring, or an expandable head to lock the angular position ofthe screw relative to the bone plate.

Variable-angle locking screws of the invention advantageously have ahead that is at least partially spherically-shaped. Thespherically-shaped portion of the head has an external screw thread onits outer surface. The profile of the screw thread follows thearc-shaped (i.e., non-linear) outer radius of curvature of thespherically-shaped portion. Each thread peak and each thread trough (orcrest and root in thread terminology, respectively) lies on a respectiveradius of curvature coinciding with or parallel to/concentric with(i.e., having the same center as) the radius of curvature of thespherically-shaped portion of the screwhead. In other words, the peaksmay lie on a “major” radius of curvature, which coincides with theradius of curvature of the spherically-shaped portion, while the troughslie on a “minor” radius of curvature, wherein the major and minorradiuses of curvature have the same center, thus forming concentriccircles. Note that this radius of curvature center is not necessarilythe center of the screwhead. In one embodiment, the thread profile hasprofile lines that intersect the center of the radius of curvature ofthe screwhead. Profile lines represent an extension of the longitudinalaxis of a cutting bit of a thread cutter as the cutting bit contacts asurface in which a thread is cut. Conventional locking screwheads, incontrast, have thread peaks and troughs (viewed in profile) that lie onrespective substantially straight, parallel lines, and the profile linesof those peaks and troughs extend parallel to each other and do notintersect the center of the radius of curvature of the screwhead (exceptperhaps the profile line of one peak or trough that happens to bealigned with the center).

To facilitate threading into bone, each of the bone screws may beself-tapping and/or self-drilling. Each of the bone screws also may becannular for insertion of a guide wire to guide screw placement.

Bone plates of the invention are not limited to any particular shape,size, or configuration. For example, in one embodiment, the bone platehas a head portion and a shaft portion. The head portion is configuredand dimensioned to conform to a metaphysis of a bone, and the shaftportion is configured and dimensioned to conform to a diaphysis of abone. In another example embodiment, the head portion has a curvedsurface and includes an anterior fork substantially parallel to ananterior side of the shaft portion and a posterior fork extending outfrom a posterior side of the shaft portion. In still another exampleembodiment, the head portion flares outward from the shaft portion andis curved, tapered, and twisted.

Bone plate holes of the invention are not limited to any particularnumber or arrangement. Optionally, bone plate holes of the invention mayhave elongated non-threaded portions to increase the versatility ofplacing non-locking screws. Bone plates of the invention may alsooptionally have suture holes and conventional threaded and/ornon-threaded screw holes, although neither type of conventional hole isnecessary nor recommended.

The invention also provides a method of bone fracture fixation. Themethod includes positioning a bone plate against bone, selecting a boneplate hole for inserting there through a bone screw, selecting anon-locking, locking, or variable-angle locking bone screw, insertingthe selected bone screw through the selected bone plate hole and, ifapplicable, selecting an insertion angle with respect to the centralaxis of the hole, and driving the screw into the bone until thescrewhead is seated in or secured to the bone plate hole to eithercompress the bone plate against the bone or fix the relationship betweenthe screw and the bone plate. The bone screws remain in the bone forsubstantially as long as the bone plate is implanted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is an elevational view of a conventional non-locking bone screw;

FIG. 2 is an elevational view of a conventional locking bone screw;

FIGS. 3A and 3B are elevational and cross-sectional views of the head ofa conventional locking bone screw;

FIG. 3C is an enlarged, partial cross-sectional view of the locking bonescrew of FIGS. 3A and 3B;

FIG. 4A is a perspective view of a rack and pinion gear;

FIG. 4B is an elevational front view of the pinion gear of FIG. 4A;

FIG. 4C is an enlarged sectional view of the pinion gear of FIG. 4B;

FIG. 5A is a perspective view of a variable-angle locking screwaccording to the invention;

FIGS. 5B and 5C are front elevational and cross-sectional views,respectively, of the head of the variable-angle locking screw of FIG.5A;

FIG. 6 is a cross-sectional view of another embodiment of avariable-angle locking screw according to the invention;

FIG. 7 is a cross-sectional view of a still another embodiment of avariable-angle locking screwhead according to the invention;

FIG. 8 is a perspective view of a portion of a bone plate withconventional locking, non-locking, and combination locking/non-lockingbone plate holes;

FIGS. 9A and 9B are perspective views of an embodiment of a bone platehole according to the invention;

FIGS. 10A-C and 10D-F are top, cross-sectional, and perspective,respectively, of two similar embodiments of a bone plate hole accordingto the invention;

FIG. 11 is a cross-sectional view of a bone plate hole according to theinvention;

FIG. 12 is an enlarged, partial cross-sectional profile view of a columnof thread segments of the bone plate hole of FIG. 11;

FIG. 13 is a perspective view of an embodiment of a bone plate systemthe range of selectable angles of a variable-angle locking screwaccording to the invention;

FIGS. 14A and 14B are perspective and elevational front views,respectively, of an embodiment of a bone plate system showingnon-locking, locking, and variable-angle screws used with a bone plateaccording to the invention;

FIGS. 15A and 15B are perspective and elevational front views,respectively, of a non-locking screw inserted through a bone plate holeaccording to the invention;

FIGS. 16A and 17B are perspective and elevational front views,respectively, of a locking screw driven into a bone plate hole accordingto the invention;

FIGS. 17A and 17B are perspective and elevational front views,respectively, of a variable-angle locking screw driven into a bone platehole according to the invention;

FIGS. 18A,B,C-23A,B,C are top, cross-sectional, and perspective views,respectively, of various features of a bone plate hole according to theinvention;

FIGS. 24A-D are top, cross-sectional, top perspective, and bottomperspective views, respectively, of a bone plate hole according to theinvention;

FIGS. 25A-C, 26A-C, and 27A-D are various perspective views of drillguides used with a bone plate according to the invention;

FIG. 28 is a perspective view of an embodiment of a bone plate accordingto the invention;

FIGS. 29A-C are perspective, front elevational, and top views,respectively, of another embodiment of a bone plate according to theinvention;

FIG. 30 is a perspective view of the underside of a bone plate accordingto the invention;

FIG. 31 is a perspective view of a bone plate applied to a bone fractureaccording to the invention;

FIGS. 32-34 are cross-sectional views of three respective embodiments ofa screwhead of a variable-angle locking bone screw according to theinvention; and

FIG. 35 is an enlarged partial cross-sectional view of a screwhead of avariable-angle locking bone screw according to the invention.

DESCRIPTION OF THE INVENTION

A bone plate system according to the invention includes a bone plate,variable-angle locking screws, non-locking screws, and optionallylocking screws. The bone plate advantageously has bone plate holeshaving discrete columns of thread segments around an inner surface ofthe hole. The bone plate may also have combination bone plate holes thathave a portion with columns of thread segments and a portion withoutthread segments or threads. Both types of bone plate holesadvantageously are constructed to receive non-locking, locking, andvariable-angle locking screws. Optionally, bone plates of the inventionmay additionally have suture holes, and while unnecessary, conventionalthreaded holes, smooth holes (i.e., holes without thread segments orthreads) and/or combination holes thereof.

FIG. 1 shows a typical non-locking bone screw 100, also known as acortex screw. Generally, any surgical bone screw having a non-threadedhead 102 with a generally smooth surface and of an appropriate size andgeometry for a selected plate hole can be used with the invention. Theshape of head 102 may be, for example, conically tapered,straight-sided, spherical, hemispherical, etc. Non-locking screw 100 hasa shaft 104 that is at least partially threaded for attachment to bone.The length of shaft 104 and the thread configuration (e.g., pitch,profile, etc.) of shaft thread 107 can vary depending on theapplication. As is known in the art, tip 106 and shaft threads 107 maybe self-tapping and/or self-drilling to facilitate implantation intobone. Head 102 and shaft 104 may also have a cannula 108 for receiving aguide wire to aid in proper placement.

FIG. 2 shows a typical locking screw 200. Generally, any surgical bonescrew having a threaded head 202 can be used with the invention providedthat head 202 is of an appropriate size and geometry for a selectedplate hole and that threads 203 mate with the columns of thread segmentsin the plate hole. The shape of head 202 is typically conically tapered,but also may be, for example, straight-sided. Locking screw 200 has ashaft 204 that is at least partially threaded for attachment to bone.The length of shaft 204 and the thread configuration (e.g. pitch,profile, etc.) of shaft thread 207 can vary depending on theapplication. As is known in the art, tip 206 and shaft threads 207 maybe self-tapping and/or self-drilling to facilitate implantation intobone. Head 202 and shaft 204 may also be cannular for receiving a guidewire to aid in proper placement.

FIGS. 3A and 3B show head 302 of a typical locking screw 300. Theprofile of thread 303 on head 302 includes thread peaks 310 and troughs312 connected to each other by flanks 311, two adjoining flanks 311forming a thread angle 317, as shown in FIG. 3C. Head 302, which isconically shaped as is usual on known locking screws, is typicallyoriented such that thread peaks 310 lie on a straight line, such aslines 313 or 315, and thread troughs 312 lie on another straight line,such as lines 314 or 316, wherein the pairs of lines (313, 314) and(315, 316) are parallel to each other. Furthermore, the thread profilelines of each thread peak 310 and each thread trough 312 extend parallelto each other and perpendicular or normal to the central axis 319 of thescrew, as represented by trough profile lines 318 a-e shown in FIG. 3B.Profile lines 318 a-e are formed by extending the longitudinal axis 301of a cutting bit 305 of a thread cutter as the cutting bit contacts theouter surface of head 302 to cut thread 303. A typical locking screwalso has a constant thread pitch (the distance from peak to peak, troughto trough, or profile line to profile line) as measured along thecentral axis (e.g., 319).

A variable-angle locking screw according to the invention has ascrewhead that is at least partially spherical. The spherically-shapedportion of the head has a thread on an outer surface thereof which ispreferably a double lead thread. The thread has a profile that followsthe arc-shaped (i.e., non-linear) radius of curvature of thespherically-shaped portion of the head. Note that the thread pitch isconstant as measured along the radius of curvature, but varies fromnarrow-to-wide-to-narrow as measured along the central axis of the screwfrom one end (e.g. the top) of the spherically-shaped portion of thehead to the other end (e.g. the bottom) (see, e.g. FIGS. 32-35 and thedescription thereof further below). This thread profile allows thevariable-angle locking screw to engage a bone plate hole of theinvention at a selectable angle within a range of angles whileadvantageously maintaining the same degree of contact with the boneplate regardless of the angle chosen. That is, the angle of the screwwith respect to the central axis of the bone plate hole within thepermissible range of angles does not affect the engagement of thescrewhead thread with respect to the inner surface of the plate hole. Atight lock is advantageously obtained between the screw and the boneplate regardless of the angle (within the range of angles) at which thescrew is inserted into the bone plate hole, because the threads on thespherically-shaped portion of the screwhead engage the columns of threadsegments in precisely the same manner, ensuring a good fit.

Some of the advantageous features of the bone plate system of theinvention may be explained with the aid of an analogy with rack andpinion gears. Although bone plate systems and rack and pinion gears arevery much unrelated (rack and pinion gears are used, for example, inautomotive steering mechanisms and locomotive and railcar drivemechanisms), the bone plate system of the invention shares an analogousconcept. As shown in FIGS. 4A-C, rack and pinion gear 400 has a rack 420having teeth 421 and a circular pinion 422 having teeth 423. Rotationalmotion applied to pinion 422 causes rack 420 to translate while,conversely, linear motion or translation of rack 420 causes pinion 422to rotate.

The analogous concept is the arrangement of teeth 423 around the radiusof curvature 425 of pinion 422. Gear teeth 423, shown in profile inFIGS. 4B and 4C, are equally angularly spaced and follow radius ofcurvature 425. Moreover, each tooth 423 is oriented such that a linebisecting the tooth 423, as represented by line 427, intersects thecenter 426 of the radius of curvature 425, which forms a circle having aradius 424. Similarly a line bisecting any space 428 between adjacentteeth 423, as represented by line 429, also intersects center 426. Thethread profile of the head of a variable-angle locking screw (viewed ina direction perpendicular to the central axis of the screw) according tothe invention is analogous to that of the sectional profile view of thepinion teeth 423 and spaces 428 of FIG. 4C.

FIGS. 5A-C show an embodiment of a variable-angle locking screwaccording to the invention. Variable-angle locking screw 500 has apartially-spherical head 502 and a shaft 504. Head 502 has a thread 503,and shaft 504 has a thread 507. Head 502 preferably has a recess 509 forreceiving a tool to drive and extract the screw into and out of bone andinto and out of a bone plate hole. Preferably, tip 506 and shaft thread507 are self-tapping and/or self-drilling to facilitate implantationinto bone. Head 502 and shaft 504 may be cannular for receiving a guidewire to aid in proper placement. FIGS. 5B and 5C show the profile ofthread 503, which advantageously follows the radius of curvature 525. Inone embodiment, the radius is about 2 mm. Respective peaks 510 andtroughs 512 of thread 503 as seen in profile are preferably separated byequal angular increments. Peaks 510 and troughs 512 are connected byflanks 511 at thread angles 517, which in this embodiment, arepreferably about 60 degrees. The thread profile lines 518 a-f extendthrough troughs 512 and result in a series of lines that intersect thecenter 526 of the radius of curvature 525. Profile lines 518 a-f areformed by extending the longitudinal axis 501 of a cutting bit 505 of athread cutter as the cutting bit contacts the outer spherical surface ofhead 502 to cut thread 503. In this embodiment, cutting bit 505 isalways normal to the outer spherical surface of head 502 as thread 503is cut. Also in this embodiment, the radius of curvature is such thatthe radius center 526 lies on the central axis 519 of screw 500.Depending on the length of the radius and the dimensions of the screw,center 526 may or may not lie on the central axis of the screw.Moreover, as the radius increases while the dimensions of the screwremain constant, the radius center will move outside the screwhead, asshown, for example, in FIG. 6.

FIG. 6 shows another embodiment of a variable-angle locking screw ofinvention. In this embodiment, screwhead 602 of variable-angle lockingscrew 600 has a larger radius of curvature 625 than screw 500. Thisresults in trough profile lines 618 a-f intersecting radius of curvaturecenter 626, which is a distance 630 (measured perpendicularly) fromcentral axis 619 of screw 600. If, for example, radius 624 is 10 mm,distance 630 may be about 8.2 mm for a 2.4 mm screw (the 2.4 mm refersto the major diameter of shaft 604). Note, however, that as the radiusof curvature increases, the screwhead becomes less and less spherical inshape, causing the thread profile to become more and more aligned with astraight line (such as, e.g., lines 313-316) as in known lockingscrewheads.

FIG. 7 shows still another embodiment of a variable-angle lockingscrewhead in accordance with the invention. Screwhead 702 has a centralaxis 719, thread 703, and a recess 709 for receiving adriving/extracting tool. As in previous embodiments, the profile ofthread 703 advantageously follows the arc-shaped (i.e., non-linear)radius of curvature 725 and includes thread peaks 710, troughs 712, andflanks 711. However, unlike previous embodiments, the thread profilelines do not intersect the center of the radius of curvature. Instead,the thread profile lines, represented by trough profile lines 718 a-f,extend parallel to each other and perpendicular to central axis 719.These lines extend in this manner because of the way in which cuttingbit 705 of a thread cutter contacts the outer spherical surface of head702 to cut thread 703, lines 718 a-f representing extensions oflongitudinal axis 701 of cutting bit 705. Functionally, this differenceresults in a less ideal screwhead/hole thread engagement. However,screwhead 702 is currently easier to fabricate than screwhead 502.

FIG. 8 shows a bone plate 800 having conventional bone plate holesincluding locking bone plate holes 832, non-locking bone plate holes834, and a combination locking/non-locking bone plate hole 836. Eachtype of hole extends from the top surface 837 completely through to thebottom bone-engaging surface 839. Locking plate holes 832 have threads833 extending around the inner surface of the hole for engaging thethreads around the head of a locking bone screw. Conventional lockingplate holes may have threads 833 extending completely through from topsurface 837 to bottom surface 839, as shown, or may alternatively havethreads extending for only a portion of the vertical distance betweenthe top and bottom surfaces of the bone plate. Non-locking plate holes834 have non-threaded or smooth inner surfaces 835 for accommodating thehead of a non-locking bone screw. Combination locking/non-locking platehole 836 increases the versatility of the bone plate by allowing thesurgeon to use either a locking screw or a non-locking screw through thehole. Combination hole 836 has one end with threads 833 around the innersurface of the hole for receiving a locking bone screw and the other endwith a smooth or non-threaded inner surface 835 for alternativelyreceiving a non-locking bone screw.

FIGS. 9A and 9B show bone plate 900 having bone plate holes 940 inaccordance with the invention. Instead of a helical thread around theinner surface 935 of the plate holes as in conventional locking screwbone plate holes, bone plate holes of the invention have discrete,vertical columns 942 of preferably thread segments arranged around theinner surface of the hole. The thread segment columns, if expanded tojoin each other (i.e. if extended completely around inner surface 935),would form a helical thread. The columns extend in a direction fromupper surface 937 to lower surface 939 and are spaced preferablyequidistantly apart around the inner surface of the hole. The number ofthread segments 921 per column can vary depending on the surgicalapplication and the dimensions of the bone plate and bone screw (e.g.,plate thickness and thread pitch). However, each column should have atleast two thread segments and preferably more to ensure a fixed angularrelationship between the screw and the plate.

Note that instead of thread segments, columns 942 alternatively may havea plurality of teeth formed thereon. The columns of teeth, if expandedto join each other (i.e., if extended completely around inner surface935), will not form a helical thread, but a series of concentric ridgesand grooves perpendicular to the central axis of the bone plate hole.While such columns of teeth can also receive non-locking, locking, andvariable-angle locking bone screws, the engagement of the teeth with thescrewhead threads of the locking and variable-angle locking bone screwsis less ideal than the engagement of thread segments with the screwheadthreads of the locking and variable-angle locking bone screws.

Bone plate holes of the invention preferably have four columns 942 ofthread segments, as shown in FIGS. 9A and 9B. However, bone plate holesof the invention alternatively may have other numbers of columns ofthread segments.

For example, as illustrated in the two embodiments of FIGS. 10A-C and10D-F, respectively, bone plate holes 1040A and 1040D of respective boneplates 1000A and 1000D each have six columns of thread segments (notethat because of the perspective shown, only three columns are visible inFIGS. 10C and 10F). The difference between thread segment columns 1042Aand thread segment columns 1042D is that the column width 1041A ofthread segments 1042A is about twice that of column width 1041D ofthread segments 1042D. More than six columns of thread segments is notrecommended, because of the increased risk of cross-threading thescrewhead threads with the thread segment columns. Conversely, boneplate holes of the invention having fewer than three columns of threadsegments is also not recommended because of the increased likelihood ofinsufficient stability at the bone/plate interface.

FIG. 11 shows a cross-section of a bone plate hole according to theinvention. Bone plate hole 1140 is formed in and extends completelythrough a bone plate 1100 from an upper surface 1137 to a lowerbone-engaging surface 1139. Hole 1040 has an inner surface 1135comprising a top portion 1144, a middle portion 1146, and a bottomportion 1148. Top portion 1144 extends from upper surface 1137 to middleportion 1146. Middle portion 1146 extends from top portion 1144 tobottom portion 1148 and preferably has the smallest diameter of thehole. And bottom portion 1148 extends from middle portion 1146 to lowersurface 1139. Top portion 1144 is unthreaded, has a preferably smoothinner surface 1143, and is preferably conically tapered inward towardthe lower surface. Bone plate hole 1140 has a shoulder 1145 at theintersection of top portion 1144 and middle portion 1146 (which is thetop of the first thread segment in each column). Shoulder 1145 may serveas a stop for the screwhead of a non-locking bone screw inserted throughhole 1140 and, in one embodiment, is angled such that it forms an angleof about 60 degrees with the central axis of the hole. Note that innersurface 1143 or upper surface 1137 may serve as a stop for the screwheadof a non-locking bone screw depending on the size and shape of the head.Bottom portion 1148 also has a preferably smooth inner surface 1149 andis preferably tapered inward toward the upper surface in the form of anundercut sphere. In one embodiment of the invention, the radius of theundercut sphere is about 1.75 mm. For a bone plate thickness of about 2mm, for example, the top portion may extend about 1 mm and the middleand bottom portions each may extend about 0.5 mm.

In this embodiment, middle portion 1146 of bone plate hole 1140 has fourdiscrete columns of thread segments 1142 on inner surface 1135. Eachcolumn 1142 is preferably inclined inward toward lower surface 1139 atan angle 1150 measured with respect to the central axis 1119. In oneembodiment, angle 1150 is preferably about 15 degrees. Each column 1142also preferably has four or five thread segments 1121. Other embodimentsmay have more or less thread segments as described above. For a boneplate hole accommodating a 2.4 mm variable-angle locking screw, thecolumn width 1141 of each thread segment is preferably about 0.35 mm.Other embodiments may have other column widths, depending on theapplication.

FIG. 12 shows a cross-sectional profile of a portion of a column 1242 ofthread segments 1221. (Note that a cross-sectional profile of analternative column of teeth, as described above, appears the same as thethread segments.) In FIG. 12, two of the five thread segments 1221 ofcolumn 1242 are shown. Column 1242 of thread segments is preferablyinclined toward the lower surface of the bone plate at angle 1250. Inone embodiment, angle 1250 is about 15 degrees. As seen in profile,column 1242 of thread segments 1221 includes peaks (or crests) 1210 andtroughs (or roots) 1212 connected to each other by flanks 1211 at threadangles 1217. Peaks 1210 preferably have a length 1252, which in oneembodiment is about 0.04 mm. Troughs 1212 preferably have a radius 1254,which in one embodiment is about 0.03 mm. Angle 1217 is preferably about60 degrees, and the bisection of troughs 1212, as represented by troughprofile line 1218, occurs at an angle 1256 of preferably about 30degrees as measured from a flank 1211. Other embodiments of bone platehole thread-segment columns alternatively may have other values ofcolumn incline angle, peak lengths, trough radiuses, thread angles, andbisection angles (which are a function of thread angle).

Advantageously, variable-angle locking bone screws of the invention canbe driven into bone and secured to the bone plate at a selectable anglewithin a range of selectable angles. FIG. 13 shows an embodiment of theinvention in which bone plate 1300 has bone plates holes 1340constructed in accordance with the invention. Each hole 1340 canadvantageously receive a variable-angle locking screw 1360, alsoconstructed in accordance with the invention, at a selectable angle inany direction within a range of angles. The range of angles forms a conehaving an angle 1362, which in this embodiment is about 30 degrees. Inother words, variable-angle locking screw 1360 can be inserted into ahole 1340 and secured to bone plate 1300 at a selectable angle rangingfrom 0 degrees to 15 degrees in any direction with respect to centralaxis 1319 of bone plate 1340.

FIGS. 14A-17B show an advantageous feature of a bone plate holeconstructed in accordance with the invention. Bone plate 1400 has atleast three bone plate holes 1440. Each hole 1440 has four columns ofthread segments 1542 and can advantageously receive any one of anon-locking, locking, or variable-angle locking bone screw.

As shown in FIGS. 14A, 14B, 15A, and 15B, a conventional non-lockingbone screw 14100 can be inserted through one of bone plate holes 1440.Non-locking bone screw 14100 has a non-threaded screwhead 14102 and athreaded shank 14104, each appropriately sized and configured for usewith hole 1440. Note that non-locking bone screw 14100 does not have tobe inserted through hole 1440 coaxially with the central axis of thehole, but may instead be inserted through hole 1440 at a selectableangle, as shown in FIG. 14B. FIG. 15B shows that screwhead 14102 doesnot engage the columns of thread segments 1542, but instead contactsshoulder 1545 of hole 1440 when fully seated therein.

FIGS. 14A, 14B, 16A, and 16B show conventional locking bone screw 14200inserted though a second bone plate hole 1440. Locking bone screw 14200has a screwhead 14202 with a thread 14203 on an outer surface therefore.Both the screwhead and thread are appropriately sized and dimensionedsuch that thread 14203 can threadingly engage and mate with columns ofthread segments 1542. In order to properly engage and mate with columnsof thread segments 1542, locking bone screw 14200 should be insertedthrough hole 1440 coaxially with central axis 1419 of the hole. Screw14200 also has a threaded shank 14204 for engaging bone. Shank 14204 isalso appropriately sized and dimensioned for insertion through hole1440.

FIGS. 14A, 14B, 17A, and 17B show variable-angle locking bone screw 1460inserted through a third bone plate hole 1440. Variable-angle lockingbone screw 1460, constructed in accordance with the invention, has athreaded shank 1404 and a partially-spherical head 1402 with thread 1403on an outer surface thereof. Screwhead thread 1403 has a profile thatadvantageously follows the arc-shaped (i.e., non-linear) radius ofcurvature of the spherically-shaped portion of head 1402. Screw 1460 isshown inserted into the third hole 1440 non-coaxially with the centralaxis 1719 with thread 1403 securely engaging columns of thread segments1542.

FIGS. 18A-24C illustrate various features of an embodiment of a boneplate hole according to the invention. Other than the formation ofcolumns around the inner surface of the hole, at least some of thesefeatures need not be used in alternative embodiments of a bone platehole according to the invention. Also note that the order in which thesefeatures are described and shown does not imply the order or steps of aparticular process for fabricating a bone plat hole of the invention. Asis apparent to those of ordinary skill in the art, there is more thanone way in which holes of the invention can be fabricated.

A bone plate hole of the invention typically starts with a circularstart hole 1865, as shown in FIGS. 18A-C. Start hole 1865 has a centralaxis 1819 and extends completely through a bone plate 1800 from uppersurface 1837 to lower surface 1839. In one embodiment, the diameter ofthe start hole is about 2.2 mm.

FIGS. 19A-C show an inner surface profile of a bone plate hole withoutother features. The profile of hole 1965 in bone plate 1900 includes aninwardly tapering top portion 1944, a protruding, inwardly taperingmiddle portion 1946, and a spherically undercut bottom portion 1948. Inone embodiment, the middle and bottom portions of the hole each extendalong the central axis 1919 by about 1 mm, and the radius of thespherical undercut is about 1.75 mm.

Another feature is an optional “X key” cutout 2065, shown in FIGS.20A-C. X key cutout 2065 is preferably pressed, cut, or stampedcompletely through the bone plate about the same central axis 1819 asstart hole 1865. In one embodiment, each leg of the “X” has a width ofabout 1.5 mm and terminates in an arc-shape having a radius of about0.75 m. In this same embodiment, the span between the ends of collinearlegs is about 4.25 mm. The X key cutout forms a cloverleaf designintended to accommodate a drill guide having a complementary drill-guidetip design, as described further below with respect to FIGS. 25A-27D.

Another feature is a preferably 12-degree relief cut 2165, as shown inFIGS. 21A-C (without any other hole features). Relief cut 2165 includeseight symmetrically cut sections 2166, two sections per quadrant, inwhich each section inclines inward at about 12 degrees from the uppersurface 2137 of the bone plate. The relief cut is made completelythrough the bone plate. In one embodiment, each relief cut axis 2119 isabout 1.1 mm from central axis 1819 of the bone plate hole.

FIGS. 22A-C show a hole profile with top portion 1944, middle portion1946, bottom portion 1948, X key cutout 2065, relief cut 2165, and fourcolumns 2242 formed therein that have not yet had teeth or threadsegments cut into them. Columns 2242 are formed by removing axialsections from the inner surface of the middle portion of the hole.

A thread cutting process forms the thread segments in columns 2242. Notethat if middle portion 1946 had not had the columns formed therein, thethread cutting process would have cut a helical thread 2367 in andcompletely around the inner surface of middle portion 2346 of hole 2365as shown in FIGS. 23 A-C. The thread profile (i.e., the peaks, troughs,flanks, and the angles formed by adjacent flanks) of the thread segmentsis preferably the same as the profile described above for the columns ofthread segments shown in FIGS. 11 and 12.

As described previously, instead of forming thread segments in columns2242, teeth may be formed alternatively therein. Teeth are formed bycutting grooves in the column that are perpendicular, or at leastsubstantially perpendicular, to the central axis of the hole. Note thatif middle portion 1946 had not had the columns formed therein, thegroove cutting process would have formed a concentric, parallel seriesof alternating grooves and ridges.

FIGS. 24A-D show a completed embodiment of a bone plate hole accordingto the invention. Hole 2440 includes columns of thread segments 2442, Xkey cutout 2065, and relief cut 2165. FIG. 24C shows top surface 2437 ofhole 2440, while FIG. 24D shows bottom surface 2439 of hole 2440 that isintended to contact, be adjacent to, or face the bone.

FIGS. 25A-27D show another advantageous feature of the invention inconnection with drill guides. One embodiment of a drill guideconstructed in accordance with the invention is shown in FIGS. 25A-26C,and another embodiment is shown in FIGS. 27A-D.

FIG. 25A shows drill guide 2570, which has a tip 2571 and a handle 2573.As shown in FIG. 25B, tip 2571 has four equidistantly spaced and roundedwings or sections 2572 forming a cloverleaf design arranged around adrill shaft for guiding a drill, a bone screw, and/or adriving/extracting tool through a bone plate 2500 and into bone at aselectable angle. Wings 2572 are sized and configured to fit snuglywithin the X key cutouts 1965 of bone plate holes 2540. This allowsdrill guide 2570 to be inserted coaxially into a bone plate hole 2540(i.e., coaxially with the central axis of a bone plate hole) and to beeasily held in place while a hole is drilled into the bone and/or a bonescrew is driven into the bone. Note that, alternatively, configurationsother than the cloverleaf design and X key cutouts can be used for tip2571 and holes 2540, respectively. As shown in FIG. 25C, handle 2573 canswivel 360 degrees about tip 2571 and the central axis of the hole 2540in which tip 2571 is inserted.

FIG. 26A shows drill guide 2570 having a slot 2675 through whichdrillings within a range of selectable angles can be made. In thisembodiment, the selectable angles range from 0 degrees to 15 degrees.The ability of handle 2573 to swivel 360 degrees thus provides a 30degree cone of angulation around the central axis of the hole. Drillguide 2570 has markings 2674 a-d along slot 2675, which in thisembodiment indicate 0, 5, 10, and 15 degrees, respectively, with respectto the central axis of the hole. Other embodiments may have other angleranges and/or other markings of selectable angles. FIGS. 26A and 26Bshow a drill bit 2676 being guided through drill guide 2570, throughbone plate 2500, and into bone 2678 at the uppermost angle setting 2674a, which in this embodiment is 0 degrees with respect to the centralaxis of the bone plate hole (i.e., coaxial). FIG. 26C shows drill bit2676 being guided through drill guide 2570, through bone plate 2500, andinto bone 2678 at the lowermost angle setting 2674 d, which in thisembodiment is 15 degrees with respect to the central axis of the boneplate hole or 75 degrees with respect to the top surface 2637 of boneplate 2500.

FIGS. 27A-D show another embodiment of a drill guide in accordance withthe invention. Drill guide 2770 has a funnel-shaped guide 2777 with atip 2771A at one end, a coaxial guide 2779 with a tip 2771B at theopposite end, and a handle 2773 there between. Tips 2771A and 2771B eachhave four equidistantly spaced and rounded wings or sections 2772forming a cloverleaf design around a drill shaft for guiding a drill, abone screw, and/or a driving/extracting tool 2776 through a bone plateand into bone. Wings 2772 are sized and configured to fit snugly withinthe X key cutouts 1965 of bone plate holes of the invention (e.g., boneplate holes 2540). This allows either end of drill guide 2770 to beinserted coaxially into a bone plate hole (i.e., coaxially with thecentral axis of the bone plate hole) and to be easily held in placewhile a hole is drilled into bone and/or a bone screw is driven intobone. Note that, alternatively, configurations other than the cloverleafdesign and X key cutouts can be used for tips 2771A and 2771B and holesof the invention, respectively. Unlike handle 2573 of drill guide 2570,handle 2773 does not swivel about either tip 2771A or 2771B. Instead,funnel-shaped guide 2777 has a funnel-shaped bore 2775 extending therethrough and centered about the central axis of the bone plate hole inwhich tip 2771A is inserted. Bore 2775 provides a cone of angulation,which in this embodiment is 30 degrees. With funnel-shaped guide 2777inserted in a bone plate hole of the invention, and thus locked in afixed position, drillings can be advantageously made at a selectableangle in any direction ranging from 0 degrees to 15 degrees with respectto the central axis of the hole. At the opposite end of drill guide2770, coaxial guide 2779 has bore 2778 extending there through. Withcoaxial guide 2779 inserted in a bone plate hole of the invention, bore2778 can be used to guide a drill bit or driving/extracting tool 2776coaxial to the central axis of the hole. Coaxial guide 2779 also has anoptional measurement gauge 2774 to help determine penetration depths.

FIG. 28 shows a bone plate configuration in accordance with theinvention. Bone plate 2800 is shaped and configured for, but not limitedto, fractures of the lateral proximal tibial plateau. Bone plate 2800has a head portion 2880 configured and dimensioned to conform to themetaphysis of the lateral proximal tibia, and a shaft portion 2882configured and dimensioned to conform to a diaphysis of the lateralproximal tibia. Bone plate 2800 further has an upper surface 2837 and aplurality of bone plate holes 2840 that extend completely through thebone plate, from upper surface 2837 to the bottom surface. Each hole2840 has four columns of thread segments 2842 and can advantageouslyreceive either a non-locking, locking, or variable-angle locking bonescrew according to the invention. Shaft portion 2882 also has severalfigure-eight shaped combination holes 2884 for increased versatility,where one portion 2885 of the figure-eight has preferably four columnsof thread segments and the other portion 2886 is preferably smooth andunthreaded. Portion 2886 can receive a non-locking bone screw, whileportion 2885 can advantageously receive either a non-locking, locking,or variable-angle locking bone screw. The ability to use variable-anglelocking screws in shaft portion 2882 is particularly useful when the farcortex of part of the diaphysis is missing or severely damaged sincefixation with non-locking screws is problematic because of the conditionof the far cortex. The particular type and placement of bone plate holesmay of course vary.

FIGS. 29A-C show another bone plate configuration in accordance with theinvention (this is same bone plate shown in FIGS. 25-27). Bone plate2900 is shaped and configured for, but not limited to, fractures of thedistal radius. Bone plate 2900 has a head portion 2980 configured anddimensioned to conform to the metaphysis of the distal radius, and ashaft portion 2982 configured and dimensioned to conform to a diaphysisof the distal radius. Bone plate 2900 further has an upper surface 2937,a lower surface 2939, and a plurality of bone plate holes 2940 thatextend completely through the bone plate, from upper surface 2937 tolower surface 2939. Each hole 2940 has preferably four columns of threadsegments 2942 and can advantageously receive either a non-locking,locking, or variable-angle locking bone screw according to theinvention. Shaft portion 2982 also has several combination holes 2984and 2989 for increased versatility. Hole portions 2985 of thecombination holes have preferably four columns of thread segments 2942and the other portions 2886 and 2887 are preferably smooth andunthreaded. Portions 2886 and 2887 can receive a non-locking bone screw,while portions 2885 can advantageously receive either a non-locking,locking, or variable-angle locking bone screw. In one embodiment, thelength 2990 of bone plate 2900 is about 65 mm, the width 2992 of headportion 2980 is about 22.2 mm, and the angle 2994 at which head portion2980 is inclined upward with respect to shaft portion 2982 is about 25degrees.

As shown in FIG. 30, bone plates of the invention preferably may beshaped to limit and/or minimize contact between the lower surface orunderside of the bone plate and the bone. Limiting and/or minimizingcontact between the bone plate and bone has a number of biological andmechanical advantages including reduced damage to blood supply andeasier plate removal. One way to limit and/or minimize contact between abone plate 3000 and bone is to provide plate 3000 with radiused orscalloped cutouts 3099 on lower surface 3039 between bone plate holes.Other ways are disclosed in U.S. Pat. Nos. 5,151,103; 5,053,036;5,002,544; and 4,838,252. The contents of these patents are incorporatedherein by reference.

FIG. 31 shows an embodiment of the bone plate system of the invention asapplied to a bone fracture. Bone plate 2900 is shown attached tofractured bone 3178 via four variable-angle locking screws 3160 insertedat various selectable angles through bone plate holes 2940 of headportion 2980 and attached to bone plate 2900 via the columns of threadsegments in holes 2940. The columns of thread segments on the innersurface of bone plate holes 2940 interact and mate with the thread onthe spherically-shaped head of variable-angle locking screws 360generally analogous to a rack-and-pinion, allowing the variable-anglescrews 3160 to be secured in plate holes 2940 at a variety of angles.Variable-angle locking screws 3160 are constructed in accordance withthe invention and may be, for example, variable-angle locking screws500, 600, and/or 700. Bone plate 2900 is also attached to bone 3178 vianon-locking bone screw 31100 inserted through portion 2987 of bone platehole 2989. Bone plate 2900 is further attached to bone 3178 via a pairof conventional locking bone screws 31200 inserted through respectiveportions 2985 of bone plate holes 2984 and secured to the bone plate viathe columns of thread segments in portion 2985. The columns of threadsegments in the bone plate holes mate with the threaded heads of thelocking screws to secure the locking screws to the bone plate. Note thatvariable-angle locking screws of the invention could have been used inplace of locking screws 31200. Note further that not all bone plateholes need to be used in each application. Variable-angle locking screws3160, non-locking screw 31100, and locking screws 31200 remain insertedthrough bone plate 2900 and into bone 3178 for as long as plate 2900remains implanted.

Returning to the screwhead thread features of variable-angle lockingbone screws constructed in accordance with the invention, FIGS. 32-34show three embodiments of a variable-angle locking screw screwhead thatillustrate the varying thread pitches (e.g., the peak to peak distance)as measured along the central axis of each screw. The following tablelists the size of the variable-angle screw to which the illustratedscrewhead belongs and the varying pitches (all dimensions inmillimeters).

FIG. 32 FIG. 33 FIG. 34 Shaft diameter: 5.0 3.5 2.4 Screwhead diameter:6.5 4.5 3.0 Pitch: 32P01 = 0.90 33P01 = 0.76 34P01 = 0.56 32P02 = 0.9533P02 = 0.79 34P02 = 0.59 32P03 = 0.99 33P03 = 0.80 34P03 = 0.60 32P04 =1.00 33P04 = 0.79 34P04 = 0.58 32P05 = 0.99 33P05 = 0.75 34P05 = 0.5532P06 = 0.95 33P06 = 0.68 34P06 = 0.49 32P07 = 0.90 33P07 = 0.60 34P07 =0.41 32P08 = 0.82 32P09 = 0.72

Other embodiments of variable-angle locking bone screws of the inventionmay have other varying thread pitches.

Note that in each case, the angular distance between adjacent threadpeaks (or adjacent thread troughs) as measured along the radius ofcurvature is constant, as illustrated in FIG. 35. That is, each angulardistance 35AD between adjacent thread peaks 3510 as measured along theradius of curvature 3525 is the same—in contrast to thread pitches35P01-35P05 which, as illustrated in FIGS. 32-34, vary as measured alongor parallel to central axis 3519.

By combining variable-angle locking screws, locking screws, andnon-locking screws on the same bone plate using the same type of boneplate hole, the invention provides a novel mixed fixation. Withnon-locking screws, fracture reduction is held by friction between thebone plate and bone. This friction is generated by tightening thenon-locking screws in bone. However, micromotion between the non-lockingscrews and bone leads to bone resorption and consequently loss ofreduction. Additionally, insertion of the non-locking screws requiresbone to withstand the stresses of screw tightening, which creates highstress in bone surrounding the non-locking screws. Ordinarily, the highstress can cause the non-locking screw threads to strip (i.e., threadsin bone fail in shear) and/or creep in bone (since bone is aviscoelastic material). Either one of these phenomenon also results inloss of reduction.

By adding at least one locking or variable-angle locking screw, loss ofreduction is minimized or eliminated. Specifically, by securing thelocking screws to the bone plate and not the bone, the effect of theviscoelastic behavior of bone is reduced, the threads do not strip, andmicromotion is prevented. The attachment between the locking screws andthe bone plate is a high strength connection of fixed angle construct inwhich the locking screw has to cut sideways through the bone to fail.

Using variable-angle screws provides an even greater advantage than thelocking screws, because the variable-angle screws may be secured at amore desirable angle than the locking screws.

Moreover, as management of certain peri-articular fractures typicallyinvolves insertion of screws at various angles with respect to the boneplate, and in view of the importance of maintaining the initial angularrelationships between the individual screws and the plate, thehighly-versatile bone plate system of the invention is particularlywell-suited for these clinical applications.

Note that the features described and illustrated herein may be usedsingularly or in combination with other features and embodiments of boneplate systems.

The invention has thus been described above in connection with thepreferred embodiments. The invention is not, however, limited to theseembodiments, which are only examples of the invention. Persons skilledin the art will appreciate that various modifications can be made withinthe scope of the invention, and the invention is limited only by theclaims which follow.

1. A bone plate system for securing a bone plate to bone, the systemcomprising a bone screw having a central axis and comprising: a shaftconfigured and dimensioned to engage the bone; a head having aspherically-shaped portion having a radius of curvature, the head havinga thread on an outer surface of the spherically-shaped portion, thethread having a profile comprising peaks, troughs, and flanks, theflanks connecting the peaks and troughs, wherein the peaks and troughslie on respective non-linear curves parallel to or concentric with theradius of curvature.
 2. The system of claim 1 wherein the thread profilehas profile lines that intersect the center of the radius of curvature,the profile lines representing extensions of the longitudinal axis of acutting bit of a thread cutter as the cutting bit contacts the outersurface of the spherically-shaped portion of the head.
 3. The system ofclaim 1 wherein the thread profile has profile lines that intersect apoint located no more than 10 mm away from the central axis measuredperpendicularly to the central axis, the profile lines representingextensions of the longitudinal axis of a cutting bit of a thread cutteras the cutting bit contacts the outer surface of the spherically-shapedportion of the head.
 4. The system of claim 1 wherein the thread profilehas profile lines that extend perpendicular to the central axis, theprofile lines representing extensions of the longitudinal axis of acutting bit of a thread cutter as the cutting bit contacts the outersurface of the spherically-shaped portion of the head.
 5. The system ofclaim 1 further comprising a bone plate having a top surface, a bottomsurface, and a plurality of holes extending from the top surface throughto the bottom surface.
 6. A bone plate system for securing a bone plateto bone, the system comprising a bone plate having an upper surface, alower bone-engaging surface, and a hole extending there through from theupper surface to the lower surface, the hole having an inner surface,wherein: the bone plate has a plurality of discrete columns of teeth orthread segments arranged around the circumference of the hole on theinner surface of the hole, each column extending in a direction from theupper surface to the lower surface; the hole is configured anddimensioned to receive a non-locking bone screw, a locking bone screw,or a variable-angle locking bone screw; and the columns of teeth orthread segments are configured and dimensioned to engage a thread on ahead of the locking bone screw or the variable-angle locking bone screw.7. The bone plate system of claim 6 wherein the bone plate has fourdiscrete columns of teeth or thread segments arranged around thecircumference of the hole on the inner surface of the hole.
 8. The boneplate system of claim 6 wherein the plurality of discrete columns ofteeth or thread segments are spaced equidistantly apart on the innersurface of the hole.
 9. The bone plate system of claim 6 wherein eachcolumn of teeth or thread segments inclines inward toward the lowersurface at an angle of about 15 degrees.
 10. The bone plate system ofclaim 6 wherein the bone plate has a top portion, a middle portion, anda bottom portion forming the hole, the top portion extending from theupper surface to the middle portion, the middle portion extendingbetween the top portion and the bottom portion, and the bottom portionextending from the middle portion to the lower surface, wherein themiddle portion has the plurality of discrete columns of teeth or threadsegments arranged on the inner surface of the hole.
 11. The bone platesystem of claim 10 wherein the top portion of the hole is unthreaded orhas a smooth inner surface.
 12. The bone plate system of claim 10wherein the top portion of the hole is conically tapered inward towardthe lower surface.
 13. The bone plate system of claim 10 wherein thebottom portion of the hole is unthreaded.
 14. The bone plate system ofclaim 10 wherein the bottom portion is tapered or curved inward from thelower surface to the middle portion.
 15. The bone plate system of claim10 wherein the discrete columns of teeth or thread segments form ashoulder at the intersection of the top portion and the middle portionof the hole.
 16. The bone plate system of claim 6 further comprising abone screw comprising a head and a threaded shaft, the threaded shaftconfigured and dimensioned to fit through the hole and to engage thebone.
 17. The system of claim 16 wherein the hole has a central axis andthe bone screw is a locking bone screw with a thread on an outer surfaceof the head configured and dimensioned to engage the plurality ofcolumns of teeth or thread segments coaxial to the central axis.
 18. Thesystem of claim 16 wherein the bone screw is a non-locking bone screwwith no screw threads on an outer surface of the head, the headconfigured and dimensioned to contact the uppermost teeth or threadsegments nearest the upper surface.
 19. The system of claim 16 whereinthe bone screw is a variable-angle locking bone screw, the head having aspherically-shaped portion having a radius of curvature, the head alsohaving a thread on an outer surface of the spherically-shaped portion,the thread configured and dimensioned to engage the plurality of columnsof teeth or thread segments, the thread having a profile comprisingpeaks, troughs, and flanks, the flanks connecting the peaks and troughs,wherein the peaks and troughs lie on respective non-linear curvesparallel to or concentric with the radius of curvature.
 20. A method ofbone fracture fixation comprising: positioning a bone plate againstbone, the bone plate having a plurality of bone plate holes, each holeextending completely through the bone plate; selecting any one of anon-locking, locking, or variable-angle locking bone screw for insertionthrough any one of the bone plate holes and into the bone; selecting anyone of the bone plate holes for inserting there through the selectedbone screw; and inserting the selected bone screw through the selectedbone plate hole and into the bone.
 21. The method of claim 20 whereinthe selecting of any one of a non-locking, locking, or variable-anglelocking bone screw comprises selecting a locking or variable-anglelocking bone screw, the method further comprising engaging threads onthe screwhead of the locking or variable-angle locking bone screw withcolumns of teeth or thread segments located on an inner surface of theselected bone plate hole.
 22. The method of claim 20 wherein theinserting the selected bone screw comprises inserting the selected bonescrew through the selected bone plate hole and into the bonenon-coaxially with respect to the central axis of the bone plate hole.23. The method of claim 20 wherein: the selecting any one of anon-locking, locking, or variable-angle locking bone screw comprisesselecting a variable-angle locking bone screw; and the inserting theselected bone screw comprises inserting the selected variable-angle bonescrew through the selected bone plate hole and into the bone at anyangle within a range of angles in any direction from a central axis ofthe selected hole.
 24. The method of claim 20 further comprising:inserting a portion of a drill guide having rounded corners withincorresponding scalloped cutouts in the selected hole; selecting adesired angle within a range of angles permitted by the drill guide atwhich to insert a bone screw through the selected hole and into thebone, the portion of the drill guide inserted into the selected holeremaining in a fixed position in the selected hole regardless of angleselected.
 25. A method of fabricating a hole in a bone plate of a boneplate system for internal bone fracture fixation, the method comprising:drilling a start hole completely through a bone plate from an uppersurface to a lower surface of the bone plate, the start hole having acentral axis, and the bone plate having an inner surface around thecircumference of the hole; forming a top portion, a middle portion, anda bottom portion in the inner surface around the hole, the top portionextending from the upper surface to the middle portion, the middleportion extending from the top portion to the bottom portion, and thebottom portion extending from the middle portion to the lower surface,the middle portion forming a smaller diameter of the hole than the topand bottom portions; removing a plurality of axial sections from theinner surface of the middle portion of the hole to form a plurality ofcolumns on the inner surface of the middle portion; and forming aplurality of grooves in each of the columns.